Chemical fruit thinners were applied to limbs or whole trees of spur `Delicious' at various stages of fruit development as indicated by fruit diameter. Carbaryl, naphthalene acetic acid (NAA), and ethephon all reduced fruit set when applied at a fruit diameter of ≈4 to 15 mm. Fruit thinning for NAA and carbaryl, alone or combined, generally was greater when applied at an average fruit diameter of 8 mm, rather than at 4 mm. Repeated applications of NAA or carbaryl were no more effective than single applications. NAA + carbaryl applied at 9 mm was more effective than NAA applied at 4 mm followed by carbaryl at 8 mm. Applied when fruit diameter averaged 17 to 22 mm, ethephon and ethephon + carbaryl were effective fruit thinners. When applied at full bloom to ≈10 and 20 mm, the insecticides ethion and oxamyl, respectively, were effective fruit thinners.
Root systems of two Magnolia taxa were treated with spray applications of auxins to determine their effects on root regeneration. Spray application of 500 ppm of IBA doubled the number of adventitious roots regenerated from the cut ends of main roots in 1-year-old cuttings of Magnolia × Soulangiana (Soul.-Bod). Higher concentrations of IBA inhibited root regeneration. Auxin applications did not increase the number of lateral or branch roots. Root systems of Magnolia × Soulangiana were treated with spray applications of ethanol to determine effect of IBA on root regeneration. A significant negative linear relationship was found between ethanol concentration and the number of adventitious roots initiated at the cut ends of main roots. Ethanol concentrations of 12.5% to 70% had no effect on the number of lateral roots. Root regeneration of Magnolia × ‘Betty’ was not stimulated with soil drench applications of 250 to 1000 ppm IBA. IBA and NAA concentrations of 1000 to 4000 ppm were inhibitory. Chemical names used: 1H-indole-3-butyric acid (IBA), 1-napthaleneacetic acid (NAA).
We propose that return flowering of `Fuji' apple can be improved if sufficient flower clusters are removed during or shortly after bloom. In this study conducted at Corvallis, Ore., we evaluated two synthetic auxins, MCPB-ethyl and the Na salt of NAA, each at 0, 4, 8 and 16 ppm, as blossom cluster thinners. Each auxin treatment was applied alone or with 100 ppm ethephon as a tank mix. Six-year-old `Fuji'/M.26 trees were sprayed at full bloom of the king flowers (≈85% of whole-tree full bloom). A follow-up treatment of Sevin XLR (800 ppm carbaryl) was made at 11-mm fruit diameter to determine if carbaryl's known effectiveness as a fruitlet thinner was influenced by the bloom-time auxin or auxin + ethephon treatments. MCPB-ethyl proved ineffective as a bloom-time thinner, whereas the NAA effect on cluster removal was linear with concentration, 16 ppm NAA completely defruiting 33% of initial flower clusters. On control trees fewer than 12% of flowering clusters failed to set fruit. Ethephon alone defruited 25% of the clusters and NAA+ethephon defruited 51% of clusters. It is notable that the NAA and ethephon + NAA treatments did not reduce fruit set on the remaining clusters, resulting in considerable need for hand-thinning. Carbaryl effectively reduced total crop load by increasing the number of defruited clusters and reducing the incidence of doubles and triples. There was evidence to suggest that its effectiveness was compromised by the bloom-time NAA and/or ethephon sprays.
The effect of temperature on uptake of C-labeled NAA was determined using detached apple leaves. Uptake by both adaxial and abaxial surfaces was measured at 15 and 35C over a 24-hotm period. Foliar absorption of NAA by the abaxial surface was greater than that by the adaxial surface. Absorption by the abaxial surface increased linearly (P < 0.001) with temperature over the range of 15 to 35C. These results are discussed in relation to fruit thinning. Chemical name used: 2-(1-naphthyl)acetic acid (NAA).
Leaf explants from ‘Sugar Daddy’ and ‘Sugar Plum’ petunia (Petunia hybrida L.) were pretreated in solutions of 0, 200, 400, and 800 mg/liter 6-benzylamino purine (BA) and were placed in a cytokinin-free modified Murashige and Skoog (MS) medium, to which 0.05, 0.1, or 0.2 mg/liter naphthaleneacetic acid (NAA) were incorporated to test interaction. NAA at 0.05 or 0.1 mg/liter increased shoot number, fresh weight, and shoot quality rating for ‘Sugar Daddy’, while in ‘Sugar Plum’ addition of NAA increased shoot fresh weight and improved shoot quality rating without any effect on shoot number.
Treatments with gibberellic acid (GA3), naphthaleneacetic acid (NAA), or their combination to Cyclamen persicum Mill. ‘Swan Lake’ plants resulted in separate, antagonistic, or cooperative effects on leaf lamina unfolding, days to flowering, number of leaves at first flower, and length of the first flower's peduncle. Generally, GA3 accelerated plant growth nonspeciflcally, resulting in plants which flowered earlier than untreated plants, but with a similar number of leaves at first bud flowering. The combination of GA3 plus NAA specifically accelerated flowering, but this effect diminished as the treatment frequency or quantity of the NAA application increased.
Emerging primocanes of red raspberry, Rubus ideaus L. ‘Boyne’, were sprayed with naphthaleneacetic acid (NAA) at concentrations of 0.5, 1.0, and 1.5% when shoots were 7–13-cm-tall or at 1.0 and 2.0% when they were 13–20-cm-tall. Treated primocanes exhibited leaf cupping and epinasty followed by withering and death. Untreated floricanes and primocanes emerging after treatment were normal. Treatment with NAA at all rates restricted the height of primocanes emerging after treatment. Fruit yield the year following was reduced by NAA applied to shoots 13-20-cm-tall.
Newly budded trees of ‘Valencia’ orange [Citrus sinensis (L.) Osbeck] on rough lemon (C. jambhiri Lush.), alemow (C. macrophylla Wester), Troyer citrange (Poncirus trifoliata Raf. ⨯ C. sinensis), and P. trifoliata were sprayed with 2 concentrations of naphthaleneacetic acid (NAA) to inhibit rootstock sprouting, buds being protected with budding tape. Good control of rootstock sprouts was obtained on rough lemon and P. trifoliata but translocated NAA inhibited scion bud initiation. There was partial suppression of rootstock sprouts on Troyer citrange but no scion bud inhibition. NAA did not control rootstock sprouts on alemow.
These studies with apple (Malus domestica Borkh.) spur tissues were conducted to investigate the mechanism whereby NAA may stimulate fruit abscission in the spring but acts to prevent fruit drop in the fall. NAA-induced ethylene evolution from `Delicious' spurs in vivo was similar to that evolved from excised leaf and fruit tissues that later were treated in the laboratory and incubated in darkness at 20C. The peak in ethylene production occurred 24 hours after treatment at 30C, 48 hours after treatment at 20C, and production was still increasing 72 hours after treatment at 10C. Leaf tissue showed the greatest induction of ethylene from NAA followed by fruit and petiolar tissues. Induction was greatest early in the season and declined steadily until about “June drop.” After this time, none of the tissues showed significant capacity for ethylene induction. Chemical names used: 2-(1 -naphthyl) acetic acid (NAA).
Biennial bearing of apple trees can be overcome either by the use of a blossom chemical thinner or by early application of a postbloom thinner. Carbaryl (Sevin) is a post-bloom fruit-thinning chemical with an effective thinning period of 4 to 5 weeks after bloom. Sevin was compared in 1992 and 1993 with NAA as an early petal-fall spray. Sevin treatments reduced fruit set to one fruit per cluster with no adverse side effects on the foliage. NAA inconsistently reduced fruit set and the remaining fruit were in clusters, The NAA-treated foliage was adversely affected; having small curled leaves. NAA at 10 ppm under-thinned in 1992 and seriously over-thinned in 1993, whereas Sevin treatments were consistent for fruit thinning in both years. Sevin applied at petal-fall or at petal-fall + 7 days effectively reduced fruit set and reduced fruit competition.